The invention refers to a method for making construction elements of light weight concrete with a binder, e.g. cement, inorganic aggregates, e.g. sand, and an aggregate of expanded foamed beads, for example polystyrene expanded beads, whereby the granules are foamed before the mixing process after which the ready concrete mix is inserted into a form for compaction.
Light weight construction elements such as gladding panels, concrete blocks and so on produced according to such a method show very attractive heat insulating properties and in many cases provide excellent sound absorption. A further noticeable advantage is the ease of handling due to reduced weight in comparison to construction elements made of normal weight concrete.
According to the prior art, plastic beads are foamed in an expanding apparatus and after aging and a certain time of storage are fed into a concrete mixer together with the other aggregates. The ready mix is then formed in ground laying machines, stationary machines or the like used for the production of standard concrete elements.
The problems that occur in such production include extremely long compaction time and a tendency of the elements to burst so that the percentage of waste goods is high.
As the inventor recognized this shortcomings are due to the fact that the foamed and fully aged plastic beads have a certain elasticity so that they are compressed during the compaction of the concrete mix and tend to reexpand after the compaction pressure dissipates. If, at that time, the binder e.g. cement has not hardened sufficiently the result is that the block cracks.
Other methods provide a pre foaming of the plastic beads and, after the aging step a final reheating step with steam in the mould. This necessitates special expensive moulds. Alternatively when the treatment occurs immediately before the mix enters the mould, an additional working step is required.
Also, in the second case, expansion of the plastic beads takes place in the mould with the resulting disadvantages as the necessity of a long holding time in the mould for the produced elements.